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X-ray supply
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From: Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent: Thursday, March 26, 1998 11:13 AM
To: Tesla List
Subject: Re: X-ray supply
> From: Hollmike [SMTP:Hollmike-at-aol-dot-com]
> Sent: Thursday, March 26, 1998 5:59 AM
> To: tesla-at-pupman-dot-com
> Subject: Re: Multi layered tesla coil
>
> Jim, all,
> A buddy of mine just got a power supply that was removed from an X-ray
> diffraction instrument. He informed me that it is rated at 60kV and
4kVA. I
> am wondering if this can be used to power a TC easily? I hope that it
was
> replaced due to some other fault than winding failure in the
transformer(it
> has some circuitry included with the tranny and I got just a vague
> description), but would like some feedback before attempting to use such
a
> tranny. I calculated that it would have 66.6 ma output. Does this type
of
> tranny have shunts that can be removed like neons to increase the current
* output?
*
Most of the X-ray circuitry I have seen relies on other techniques to keep
the current constant. For accurate xray work, you need to have a fairly
constant voltage and a fairly constant beam power, which a simple series
inductor won't do (magnetic shunts are equivalent to a big series
inductor). The series inductor is really nice for gas discharge
applications with a pronounced negative V/I characteristic: neon tubes, arc
lamps, welding, spark ignitions.
You might want to make sure that the transformer is designed to work at 60
Hz. My GE xray power supply runs at 500 Hz, dramatically reducing the
amount of iron required in the core and making the whole system a lot
lighter weight.
> I know that I can make a series cap to withstand the voltage, but
will
> corona losses cause serious problems in design of such a system? I
figure I
> would use at least 0.5" copper tubing for all primary connections and the
> primary coil to reduce the stresses, but will this be enough?
A rule of thumb is allow 1 inch clearance for every 10 kV (7 times the
breakdown distance), and to make the radius of curvature 1 inch for every
40 kV. (about twice the theoretical minimum radius) (That's the RADIUS, so
for 60 kV, you should really be looking at 2 or 3 inches in diameter).
Perhaps you might want to run it in oil?
More on corona at http://home.earthlink-dot-net/~jimlux/hv/corona.htm
Corona and breakdown is also aggravated by objects near the hv object,
conducting or not. For instance, the breakdown voltage between a flat plate
and a needle is larger than the breakdown between two needles. An
insulating column between two flat electrodes can reduce the break down
voltage (through the air along the surface of the column) by a factor of 3.
That is, the creepage distance needs to be several times the flashover
distance.
The moral of the story is that an inch of air will stand off the 60 kV, if
it were a flat plate with nothing other than air. When it is a curved
surface with bumps, and there are insulating supports, etc. you'll need
more distance.
> My buddy lives in New Jersey and I live in Colorado, so I need to get
as
> much input as possible before I go to the expense of having this shipped
out
> here.
And of course, you know that thinner air (e.g. at 5000 ft) has a lower
breakdown voltage than sea level air. That's why your oscilloscope is only
specified to work to 10,000 ft.